The overall objective of this project is to investigate the normal metabolic biochemistry of carnitine during development. Our aims are to answer the following questions. What are the capabilities of the newborn to synthesize carnitine in the absence of oxogenous carnitine? What are the factors which initiate and control the increase in tissue carnitine levels during early development of the rat, and what are the factors which determine the different carnitine levels in plasma, heart, and muscle, of female rats versus male rats as they reach adulthood? The biosynthetic capability of the newborn rat appears to be very limited due to undetectable levels of gamma-butyrobetaine hydroxylase activity which is the last enzyme of the carnitine pathway. At least three factors regulate the tissue carnitine levels in rats. T factor is synthesized in the testes and is either testosterone or a metabolite of testosterone. O factor is synthesized in the ovaries and is either estradiol or a metabolite of estradiol. P factor or factors is synthesized by the pituitary and has functions other than regulation of testosterone and estradiol production by the testes and ovaries. We do not know the identity of P factor, but our working hypothesis is that P factor is prolactin.